Green Technology - What Is Thermal Energy Storage? Green Technology - What Is Thermal Energy Storage?

Thermal energy storage is an example of green technology that makes use of solar radiation to provide natural heating for your home.

What is Thermal Energy?

“Thermal” energy refers to heat energy and is defined as that part of the solar spectrum of electromagnetic radiation within the infra-red (long-wave) range which produces heat. This solar radiation is absorbed and stored within the building’s structure, particularly within building materials that possess high heat storage capacity. After a short period (typically measured in hours), the absorbed heat is re-radiated to the building’s interior.

Ideally, heat is re-radiated during the evening hours when outside air temperatures approach the lower extreme and the heating load on the mechanical equipment is highest. The natural heat gain will warm the building’s interior, reducing the required energy produced by heating equipment and therefore energy costs. If designed properly, this thermal storage pattern develops into a repetitive cyclical process—absorbing heat each day from the midday sun and dispersing heat in the cool of the evening.

There are several factors that will enhance or contribute to the thermal performance of the heat storage cycle. This article will discuss ways to maximize the effectiveness of the thermal storage capability that can be implemented in the average home.

Thermal Storage Capability Depends on Building Materials

Thermal or heat storage capacity is a material property that is found by multiplying the material’s specific heat by its density. The heat storage cycle is generated by building materials with a high heat storage capacity. For this reason, massive materials like stone and concrete work best when devising a thermal storage strategy.

The thermal mass contained in high-mass materials is integrated into building elements (interior or exterior walls, floors) designed to have direct or indirect access to sunlight. The delay or “time-lag effect” is determined by the volume or thickness of the thermal mass material. For example, a larger wall thickness will delay solar penetration until later in the evening, but the amount of radiated heat is diminished.

The amount of heat gain or the rate of heat flow resulting from thermal storage can be calculated by using the material’s thermal conductivity, heat storage capacity and thickness in the basic heat conduction equation. It is the objective of the designer to combine the thermal properties and the time-lag effects of various building materials for optimal performance of the thermal storage cycle.

Additional Thermal Storage Methods

The Trombe wall is an option to those who are willing to sacrifice aesthetics for increased energy efficiency. It consists of a massive wall material such as concrete combined with a vented air space behind a layer of glazing on the exterior surface. The insulative effect of the glazing allows the wall material to absorb and retain additional heat.

Other techniques utilize earth mass storage in which the structure is partially submerged or integrated with the earth, or roof pond mass storage that uses water as the heat storage medium. These methods use the same basic heat storage principles but incorporate different elements into the thermal storage design.

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